1. Field of the Invention
The present invention relates to a reflection characteristic measuring apparatus for measuring the gloss of a sample surface.
2. Description of the Background Art
Conventionally, there is known a reflection characteristic measuring apparatus for measuring the gloss of a sample surface. FIG. 10 is a diagram showing a construction of a conventional reflection characteristic measuring apparatus 100. The reflection characteristic measuring apparatus 100 includes an incident-side optical system 101 and a reflection-side optical system 102. In the reflection characteristic measuring apparatus 100, light is irradiated toward a sample surface S from the incident-side optical system 101 disposed at a position with a certain angle with respect to the normal G passing a certain point on the sample surface S. Then, the reflection light from the sample surface S is incident to the reflection-side optical system 102 disposed at a position with a certain angle with respect to the normal G.
The incident-side optical system 101 and the reflection-side optical system 102 have diaphragms 103 and 104, respectively. The diaphragm 103 of the incident-side optical system 101 is adapted to direct the light from a light source 105 toward the sample surface S within a predetermined opening angle. The diaphragm 104 of the reflection-side optical system 102 is adapted to direct the reflection light from the sample surface S toward a light receiving surface of a light detector 106 within a predetermined light detection angle. The gloss of the sample surface S is measured, using an output from the light detector 106 which has received the thus-regulated reflection light.
Japanese Patent No. 3,185,031 discloses an arrangement concerning the aforementioned type of reflection characteristic measuring apparatus, wherein a line sensor is provided as a light detector for receiving reflection light from a sample surface to be measured so that specular reflection light from the sample surface forms a focal point on the line sensor. With use of the apparatus, the gloss of the sample surface is measured by detecting a light amount distribution concerning reflection light incident onto the line sensor.
In use of the reflection characteristic measuring apparatus shown in FIG. 10, as shown in FIG. 11, if the setting position of the sample surface S is tilted by the angle θ, the direction along which the reflection light from the sample surface S is incident to the reflection-side optical system is tilted by the angle 2θ with respect to the original condition before the tilting. In FIG. 11, the diaphragm 104 and the light detector 106 are not illustrated. In this condition, as shown in FIG. 12, assuming that the focal length of a lens element 107 of the reflection-side optical system 102 through which the reflection light is directed toward the light detector 106 is defined as f, the focusing position is displaced by f×tan 2θ on the focusing plane from the focusing position M of reflection light obtained in a condition that the sample surface S is not tilted.
In the conventional measuring apparatus 100, the dimensions of the aperture of the diaphragm 104 provided in the reflection-side optical system 102 are fixed. Accordingly, if the sample surface S is tilted as mentioned above, the amount of reflection light detected by the light detector 106 is varied with respect to a proper condition where the sample surface S is not tilted relative to the measuring apparatus 100. This results in failure of accurate detection of the gloss of the sample surface S.
Also, even if the sum of the amount of reflection light detected by the light detector 106 is identical concerning sample surfaces whose gloss is to be measured, the sample surfaces include sample surfaces having a relatively small ratio of specular reflection light component to diffusion light component as shown in FIG. 13A, and sample surfaces having a relatively large ratio of specular reflection light component to diffusion light component as shown in FIG. 13B. The curves (1) and (2) in FIGS. 13A and 13B show magnitudes of intensities of reflection light with respect to a distance from the reflection point Z. As is obvious from FIGS. 13A and 13B, the intensity of reflection light passing a relevant point on the curve (1), (2) is increased, as the distance from the reflection point Z to the point on the curve (1), (2) is increased.
In the conventional reflection characteristic measuring apparatus 100, the dimensions of the aperture of the diaphragm 104 provided in the reflection-side optical system 102 are fixed, and the gloss of the sample surface is measured based on the sum of light passing through the aperture. Accordingly, if the sum of the amount of reflection light detected by the light detector 106 is identical concerning the sample surfaces to be measured, all the sample surfaces are determined to have the same degree of gloss, which makes it impossible to distinguish the sample surfaces one from another. Even with use of the method disclosed in the above publication, the drawback cannot be overcome.